In a post or a page (block editor)
- Open the post or page and click the + button (block inserter).
- Search for Custom HTML and add the block.
- Paste the code. The Preview tab of the block shows the widget.
- Click Update or Publish.
In a sidebar or a footer
With a classic theme, go to Appearance > Widgets, add a Custom HTML block to the sidebar or footer area, and paste the code. With a block theme, open Appearance > Editor, edit the template part (header, footer) and add the same Custom HTML block. In page builders such as Elementor, use their HTML widget.
WordPress.com and plans
On a self-hosted WordPress site, administrators and editors can paste an iframe without any restriction. On WordPress.com, tags such as iframe only work on a paid plan with hosting features active (the plans that allow plugins). On the free plan, the block keeps the text but strips the widget. In that case, a simple link to the tool on Clooock is the alternative.
Why no plugin?
A plugin adds code to every page of the site, needs updates and sometimes slows down the admin. The widget is an iframe: it loads only on the page where you put it, after the rest of the page, and nothing changes in your WordPress install. To change it later, edit the address in the block or make a new one here.